An infinite variable transmission is a for of a traction drive which is a device whereby torque is transmitted from one smooth rolling element to another and typically the rolling elements are in nominal point or line contact. Variable speed traction drives can be made by proper selection of the number, size, shape and geometrical configuration of the roller elements typically comprising one or more parallel cylindrical elements spaced apart from one another. Variable speed transmissions provide a means for smooth and quiet operation and increased fuel efficiency.
For example, infinitely variable transmission (“IVT”) are configured to provide a continuous range of ratio from reverse through stationary to high overdrive utilizing a variator comprising a set of discs and rollers. The rollers do not touch the discs and there is no metal to metal contact, but are separated by traction fluid.
The variable speed transmission, (traction fluid), behaves as a lubricant and coolant in the variable speed transmission. The fluid is required to exhibit high pressure and high shear conditions found I the area of contact between the plate or roller elements which are separated by a thin film of the fluid. The fluids resistance to shear provides the torque transmitting ability of the fluid composition. The torque transmitting ability of the fluid composition can be measured by its traction coefficient.
Traction fluid works by rolling the edge of the roller against the surface of the discs which traps a microscopic oil film between them. The long chain molecules of the traction fluid interlock with one another when the fluid is compressed and becomes highly viscous under pressure. Thus, as pressure is exerted at the contact points between the roller and/or discs the oil “traction fluid” resists the tendency to slip and transmits the power effectively.